In the past light emitting diodes (LEDs) were limited to power levels under a watt. LEDs are now available in packages over five watts. LEDs are now also available with efficiencies of 100 lumens/watt. These recent advancements have enabled many new applications for LEDs. One example is the use of LEDs for warning devices such as beacon lights. Beacon lights typically emit light with a limited vertical beam spread and at all radials throughout the omnidirectional 360°. More specifically LEDs can be used in strobing beacon applications where xenon strobe tubes were used in the past. Using LEDs (light emitting diodes) to produce warning devices which produce a flash similar to the units employing xenon flashtubes have been discussed. In many applications these devices are positioned on the tops of radio transmission towers, wind turbine generators, refinery stacks, and the like. Such locations make the performance of routine maintenance (such as replacing the flashtube) extremely difficult. The ability to use LEDs with their longer lifetime in place of the xenon tube provides a major advantage.
To provide light output in these devices similar to the xenon flashtube requires a large number of LEDs. For example the Federal Aviation Administration requires the operation of white flashing devices at the tops of radio towers during daylight hours. For medium intensity applications, such devices must be capable of producing a minimum of 20,000 effective candelas of light output. To produce this light output using LEDs may require approximately 400 five watt LEDs. Because the light is flashing the LEDs would be run at a duty cycle of less than 100%.
Packaging this large number of LEDs in the small space required for a light signal results in a large concentration of heat. Buildup of heat in an LED die can lead to shorter lifetimes and, in extreme cases, failure of the LED device. Internal die temperatures for LEDs should be kept low in order to maximize the performance and lifetime of the LEDs. Maximum LED die temperatures range from about 125° C. to 150° C.